In response to RFA-AG-11-010, Basic Research on Self-Regulation, the current proposal takes an interdisciplinary approach to developing and piloting a novel functional magnetic resonance imaging (fMRI) paradigm for assessing adolescents' reward function in neural circuits implicated in reactivity and self- regulation. The overall goal of the proposed study is to develop methods for assessing the mechanisms of the development, during adolescence, of reward-related problem behaviors such as substance use, sensation- seeking, depressive symptoms, and HIV-risk behavior. Ultimately, the proposed study may have relevance to preventing these problems from developing into serious health problems such as addiction, depression, and HIV. The novel fMRI paradigm designed in the proposed study will be more ecologically valid than current fMRI reward paradigms because it will focus on personally relevant peer contexts, which create demands for the self-regulation of reward function. After development of the fMRI paradigm, the proposed study will examine 70 healthy community adolescents' neural response to the task in the striatum and medial prefrontal cortex (mPFC), as well as functional connectivity between these regions. The proposed study will investigate the association between adolescents' neural response to the novel fMRI task and their neural response to established reward tasks; behavioral response to computer tasks; behavioral response to interactions with peers; and subjective experience of positive affect during ecological momentary assessment. This strategy will allow the evaluation of how well the novel task improves on current measures of reward function. Finally, the proposed study will test the association of the novel fMRI task with adolescents' current problem behaviors relevant to the self-regulation of reward, including sensation-seeking behavior, substance use, depressive symptoms, and HIV-risk behavior. In all, the proposed study offers the opportunity to investigate how well a novel fMRI paradigm captures adolescents' reward function and predicts problem behaviors, with ultimate applications to investigating the mechanisms of the longitudinal development of serious problem behaviors.